Not applicable.
1. Field of Invention
This invention relates to photo-visual telescope filters, specifically to an improved way of filtering images of planets, the moon and daytime views.
2. Description of Prior Art
Telescope users commonly enhance images by using transparent colored photo-visual filters. Such filters reduce glare and increase the contrast and resolution of both lunar and planetary views. Daytime filter use in spotting scopes can eliminate color flinging around bright objects and improve the contrast of images. These filters are used in visual, photographic and CCD (charge coupling device) imaging applications.
The most common photo-visual filter consists of a flat, circular, dyed glass element which is mounted in a metal cell 12, as shown in prior art FIG. 1. The filter is threaded to the bottom of a telescope eyepiece 10, also shown in prior art FIG. 1. The filtered eyepiece is then inserted into the telescope eyepiece holder, shown as 14 in FIG. 1, at the back of a telescope. Filter cells are printed with numbers, indicating the color. For example, please refer to the Wratten numbers on page 78 of The Backyard Astronomer""s Guide by Terence Dickinson and Alan Dyer, printed in 2000. They can be combined to mix colors of filtration.
Telescope users find the design of filtration just described as flawed:
(a) Users are required to keep a large selection of individual colored filters in many colors of the visual spectrum, making telescopic astronomy costly and complicated.
(b) Changing filters during a viewing session increases the chances of damage to filters and eyepieces. Filters and eyepieces can drop, break, smudge or scratch while being handled in dark or low light conditions. Damage to filters and telescope eyepieces can occur because these filters must be manually threaded onto or off of eyepieces many times during a viewing session, sometimes with gloved hands in the winter season.
(c) Exposing filters to open air conditions can make them dirty or dusty, negatively effecting an image and requiring frequent cleaning.
(d) The letters or numbers that indicate the colors of individual filter cells are difficult to read due to their small size, which is approximately 3 mm in height.
(e) Determining individual colors is difficult, requiring the user to memorize or refer to a confusing numbering system, as shown in the Planetary Filter Chart on page 78 of The Backyard Astronomer""s Guide by Terence Dickinson and Alan Dyer, printed in 2000.
(f) Cross-threading damage to an eyepiece or filter can occur during changes. The chances of damage are increased when two or more filters must be combined to get a blended color.
The True Technology Ltd. Custom Wheel is an example of a complex photo-visual filter holder. It can be seen online at http://www.truetech.dircon.co.uk/True%20Technology/custom%20wheel/thewheel.html. A simplified illustration of this system is shown in prior art FIG. 2 and prior art FIG. 3. The filter holder (prior art FIG. 3) must revolve to change the individual filter color. Filters can be rotated by manual turning or by hand controller with the addition of a computer program. Problems of these systems include the need for expensive filter holders and housings. In addition, several individual colored filters must be obtained. Motors, hand controllers, computers, and software are also needed. Weight can also be a factor, which might make a telescope""s delicate balance system need rebalancing.
In accordance with the present invention a photo-visual filter comprises a variable, colored filter disc, mounted in a lightweight enclosure.
Accordingly, besides the objects and advantages of photo-visual filters in telescope usage described above, several objects and advantages of the present invention are:
(a) to provide a variable photo-visual filter that will replace many individual photo-visual filters;
(b) to provide a photo-visual filter which can be varied by rotation of a knob;
(c) to provide a variable photo-visual filter which provides easy identification of the color in use;
(d) to provide a variable photo-visual filter which is protected from handling;
(e) to provide a variable photo-visual filter which is lightweight;
(f) To provide a variable photo-visual filter which is inexpensive to manufacture, passing on savings to the consumer; and
(g) To provide a variable photo-visual filter which is easy to use, without the need for motors, computers or complex designs.
Further objects and advantages are to provide a photo-visual filter design that can be varied slightly in size or dimension, compatible with many different telescopes, spotting scopes and microscopes. Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.